Relationships between gross primary production, green LAI, and canopy chlorophyll content in maize: Implications for remote sensing of primary production

- GPP/total chlorophyll (Chl) and GPP/green LAI relationships were established.
- Green LAI and total canopy Chl content explained > 90% of GPP variation.
- The relationships had different slopes in vegetative and reproductive stages.
- The mechanisms for hysteresis of GPP vs. GLAI/Chl relationships were suggested.

Life on Earth depends on photosynthesis. Photosynthetic systems evolved early in Earth history, providing evidence for the significance of pigments in plant functions. Photosynthetic pigments fill multiple roles from increasing the range of energy captured for photosynthesis to protective functions. Given the importance of pigments to plant functioning, greater effort is needed to determine and quantify the relationship between gross primary production (GPP) and canopy chlorophyll (Chl) content, the main photosynthetic pigment, as well as its proxy, green leaf area index (GLAI), both used as quantitative measures of plant greenness. The objective of this study is to establish relationships for GPP vs. canopy Chl content and GPP vs. GLAI in maize. The main focus of the paper is to reveal fine details of the relationships and understand their features in different stages of maize development. Data on GPP, leaf Chl content and GLAI were collected across ten years (2001-2010) at three AmeriFlux sites in Nebraska over irrigated and rainfed maize. Relationships of GPP vs. total canopy Chl content and GPP vs. GLAI were established for vegetative, tasseling and reproductive stages. In each stage, relationships were close with determination coefficients above 0.9; however, the shapes and slopes of the relationships in vegetative stages were different from reproductive stages. This difference was more pronounced for the GPP vs. GLAI relationship. In part, this difference is due to different leaf Chl contents in vegetative and reproductive stages. Smaller but detectable differences in shape and slope were also found for the GPP vs. canopy Chl relationship. Despite the differences in relationships for vegetative and reproductive stages, for the entire growing season, green LAI (GLAI) explained 90% of GPP variation with a coefficient of variation (CV) = 17%, while total canopy Chl content explained more than 92% of GPP variation with CV = 15%. Quantitative characterization of relationships between GPP and such biophysical characteristics as GLAI and canopy Chl content underlines the role of chlorophyll in photosynthesis and has significant implications on remote sensing of primary production.